Atomic History - Page Text Content

1: What is the Atomic Theory? | Theories that describe the structure, behavior, properties, and component parts of the atom

2: 400 B.C. Democritus' Ideas | * Matter mainly consists of empty space where atoms move *Atoms are indestructible and invisible *Atoms come is different shapes and sizes *When groups of atoms change they cause a change in matter. *The different sizes, shapes, and movement of atoms cause different properties of matter.

3: 384-322 B.C. Aristotle | * Assumed that all substances were compounds of four elements including, air, water, earth, and fire. *These elements would combine into hot, cold, wet, and dry. *Focused on how things presented themselves to the sense. *Tested his theories through experiments by seeing how these certain element reacted with each other. For example when water is heated it evaporates.

4: 1777 Lavoisier | * Founder of modern chemistry. *Clarified that an element is a simple substance that cannot be broken down. *Showed that reactants and products are conserved in reactions. Otherwise known as the Law of Conservation of Mass *Discovered that water was made of hydrogen and oxygen.

5: 1776-1844 John Dalton's Ideas | * Matter is composed completely of extremely small particles called atoms *Atoms of the same element are identical in size, mass, and chemical properties. *Atoms of an element are different from atoms of another element *Atoms are neither created nor destroyed, or divided into smaller particles. *In whole number ratios atoms combine to make compounds. *Within a chemical reaction atoms combine, rearrange,and separate.

6: 1830 Michael Faraday | * Set up a pair of metal plates, connected by a series of batteries, in a tube filled with glass. *When he decreased the gas pressure, the gas began to glow. *In 1858 Julius Plucker noticed that only one end of the tube produced light. In addition when he moved a magnet closer to the tube, the light would move. *Because of the magnet, they were able to conclude that whatever produced the glow had a negative charge.

7: 1860's Mendeleev | * Began to work on the periodic table of elements. * Arranged all 63 elements in groups based on their similar properties. * Where a gap existed, he predicted that new elements would be discovered one day. *Three gaps were filled during his lifetime when gallium, scandium, and germanium were discovered.

8: 1870's Crookes | * Was able to create a better vacuum tube. * The tube allowed him to create cathode-ray tubes. * Studied the deflection of the cathode-rays using a magnetic field. * Concluded that the cathode rays are negatively charged.

9: 1898 J.J. Thomson | * In multiple experiments meant to study electrical discharge the the cathode-ray tube, he discovered the electron. * Proved that cathode "rays" weren't actually rays but instead particles. *Electron was originally called "corpuscles" by Thomson. *The electrons he discovered are the fundamental unit of negative electricity. Plum Pudding Model: *Matter has an overall neutral charge. *Electrons are lighter than atoms. *Thomson concluded that there must be a positively charged particle that gives the atom its weight.

10: 1900 Max Planck | * Originated the Quantum theory with the help of many other physicists. *Showed that energy is always emitted or absorbed in discrete units, which he called quanta.

11: 1905 Albert Einstein | * Considered one of the fathers of the Atomic Age. *Creator of the theories of Relativity. *Proved that mass and energy are equivalent through the equation E=mc^2 (Energy=mass times the velocity of light squared). *Theory brought new concepts of space, time, mass, gravitation, and motion.

12: * Using a "falling drop method" he determined the accurate charge of an electron. *Proved the charge was constant for all electrons, allowing him to find the atomic structure of electricity. *Extended the ultraviolet spectrum farther than anyone knew possible. | 1908-1917 Robert Millikan

13: 1909-1911 Ernest Rutherford | * Previous scientists thought that the atom was solid, Rutherford was able to prove otherwise. * Through experiments Rutherford proved that the atom was not solid. *Instead the atom consisted of a small dense region, called a nucleus, in which electrons orbit in circles. * By studying the deflection of alpha particles he was able to estimate that the positive charge of the atom was approximately half of the atomic weight.

14: 1885-1962 Neils Bohr | *Refined Rutherford's model and introduced the different orbits that electrons orbit around the nucleus. *Argued that electrons have a fixed amount of energy which determines its fixed orbit. *Therefore when an electron gains energy then it will also go to a higher orbit as well.

15: Erwin Schroedinger-1926 | * Built on Bohr's ideas * Developed the probability function which describes where an electron is most likely to be. *Model based on the probability function is called the cloud model. *The cloud model describes where an electron has most likely been and where it is most likely to go.

16: James Chadwick 1931 | * Measured the energy of the protons in the hydrogen atoms. *Proved that neutrons, that make up half the mass of an atom, do exist. *Determined that the neutron's mass was about .1 percent more than a protons mass. *Published his findings in his first paper called, "Possible Existence of Neutron."